add binarySearch

snippets/binarySearch.md

@@ -0,0 +1,23 @@
+### binarySearch
+
+Use recursion to perform a logarithmic search similar to `.indexOf()` that finds the index of a value within an array. The two differences being 
+1. Operation only works with sorted arrays
+2. Offers a major performance boost when compared to a linear search or `.indexOf()` 
+
+```js
+const binarySearch = (arr, val, start = 0, end = arr.length - 1) => {
+  if (start > end) return -1;
+  const mid = Math.floor((start + end) / 2);
+  const target = arr[mid];
+  return (target > val) 
+      ? binarySearch(arr, val, start, mid - 1)
+      : (target < val) 
+        ? binarySearch(arr, val, mid + 1, end)
+        : mid
+}
+```
+
+```js
+binarySearch([1, 4, 6, 7, 12, 13, 15, 18, 19, 20, 22, 24], 6); // 2
+binarySearch([1, 4, 6, 7, 12, 13, 15, 18, 19, 20, 22, 24], 21); // -1
+```